1. Field of the Invention
The present invention generally relates to an exhaust manifold configuration that improves the output performance and exhaust performance of an internal combustion engine.
2. Background Information
Many internal combustion engines have an exhaust manifold with a single exhaust tube extending from each cylinder. The exhaust tubes are typically merged together. This merger of the exhaust tubes can result in exhaust interference and reduced output depending on the exhaust order of the merged cylinders and the position where the exhaust tubes are merged.
Japanese Laid-Open Patent Publication No. 59-188022 discloses an engine exhaust manifold for a four cylinder in line engine. The exhaust manifold disclosed in this publication merges the exhaust tubes of cylinders having non-successive firing order first, i.e., cylinders #1 and #4 and cylinders #2 and #3. However, in recent years, the demand for improved exhaust performance of internal combustion engines has created a need for the catalyst to be held directly below the exhaust manifold. In such an arrangement, the distance from the exhaust ports of the internal combustion engine to the catalyst can be very shorten. Consequently, when it is attempted to merge the exhaust gases from cylinders #1 and #4 together and the exhaust gases from cylinders #2 and #3 together before merging with the collector case, the exhaust tubes must be merged immediately downstream of the exhaust port outlet. This arrangement leads to the problem of reduced output caused by exhaust interference.
Japanese Laid-Open Patent Publication No. 7-63092 discloses an engine exhaust manifold having two manifold catalytic converters. One of the manifold catalytic converters is provided for the exhaust tubes extending from cylinders #1 and #4. The other manifold catalytic converter is provided for the exhaust tubes extending from cylinders #2 and #3. Thus, the exhaust tubes of cylinders #1 and #4 are merged into a separate manifold catalytic converter from the exhaust tubes of cylinders #2 and #3. With this arrangement, there is little exhaust interference and no reduction of output, but there is the problem of increased cost resulting from using two manifold catalytic converters.
It is also necessary to install an air-fuel ratio sensor, typically an oxygen sensor, in the exhaust manifold in order to utilize the catalyst effectively. The air-fuel ratio sensor needs to be installed in a position where it can uniformly detect the exhaust gas from all of the cylinders. However, in the case of a manifold catalytic converter that is disposed directly below the exhaust manifold, it is becoming difficult to install the air-fuel ratio sensor such that it can uniformly detect the exhaust gas from each cylinder.
Japanese Laid-Open Patent Publication No. 6-241040 discloses an engine exhaust manifold with a collector case that is divided into two chambers by a partitioning wall such that at the exhaust gases from cylinders #1 and #4 are merged into one chamber and the exhaust gases from cylinders #2 and #3 are merged into the other of the chambers. The air-fuel ratio sensor is then arranged in an air communication passageway provided through the partitioning wall. The problem with this arrangement is that, under high load conditions in which the exhaust gas flows at a high speed, the mainstream of the exhaust gas passes through the collector case without much flow toward the communication passageway. Thus it is difficult for the air-fuel ratio sensor to uniformly detect the exhaust gas from each cylinder.
Japanese Laid-Open Patent Publication No. 11-13468 discloses an engine exhaust manifold that uses ribs in the exhaust tubes in order to direct exhaust gas toward the air-fuel ratio sensor. The problem with this arrangement is that the output declines because of these ribs in the exhaust tubes.
In view of the above, there exists a need for an improved exhaust manifold configuration that improves the output performance and exhaust performance of an internal combustion engine. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.
In view of the aforementioned problems, one purpose of the present invention is to provide an exhaust manifold that can suppress exhaust interference and improve output even in cases where a manifold catalytic converter is used close to the collector case. Another purpose of the present invention is to provide an exhaust manifold in which it is possible to install an air-fuel ratio sensor in a position where it can uniformly detect the exhaust gas from each cylinder so that the catalyst can be utilized effectively and emissions can be reduced.
In order to achieve the aforementioned purposes an exhaust manifold of an internal combustion engine is provided that comprises a collector case and a plurality of exhaust tubes. The collector case has an upstream end and a downstream end. The exhaust tubes have inlet ends that are adapted to be connected to exhaust ports of the internal combustion engine and outlet ends that are connected to the upstream end of the collector case by merging portions. The outlet ends of the exhaust tubes include linear portions disposed contiguously with the merging portions where the exhaust tubes merge with the collector case. The exhaust tubes have first exhaust tubes with the inlet ends of the first exhaust tubes arranged to receive exhaust gas from cylinders whose firing orders are not successive. The linear portions of the first exhaust tubes, whose firing orders are not successive, are slanted with respect to each other such that the linear portions of the first exhaust tubes, whose firing orders are not successive, have center axes intersecting at a point inside the collector case or downstream thereof.
These and other objects, features, aspects and advantages of the present invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses a preferred embodiment of the present invention.